Dielectric composition



Filed May 17, 1943 lmy Patented June 5, 1945 DIELECTRIC COMPOSITIONJames Franklin Hyde, Corning, N. Y., assigner to Corning Glass Works,Corning, N. Y., a corporation oi New York Application May 17, 1943,Serial No. 487,375

9 Claims.

This invention relates to dielectric liquids for electrical apparatus.

This application is a continuation-in-part of my co-pending applicationSerial Number 432,- 528 tiled February 26, 1942.

In electrical apparatus such as transformers, capacitors, cables,switches, fuses, reactors, regulators, circuit breakers, and similarequipment, it is customary to provide a liquid insulating medium whichis termed the dielectric liquid." This liquid has a substantially higherbreakdown strength than air and, by displacing air from spaces in theelectrical equipment between conductors, and to ground, materiallyraises the break-down voltage of the equipment. In the past it has beencustomary to use petroleum products, such as the mineral oils, asdielectric liquids. These oils have not proven generally satisfactory,Although possessing certain advantages by reason of their availabilityand relaltively low cost the mineral oils also possess certain veryserious disadvantages.

One disadvantage of the mineral oils is that they tend to form deposits,generally known as "sludge during the period of their use. This is dueto oxidation anddecomposition and also results to some extent in theformation o'f acids which is equally undesirable. dielectric oils duringuse is a serious disadvantage and requires either replacement of the oilor treatment to remove the sludge.

The most seriousdisadvantage of the mineral oils is the fact that theyare inflammable and upon decomposition yield gases which are alsoinilammable and explosive when mixed with air. A fire proof insulatingliquid would be highly desirable, since there exists the possibilty of anre in the eventa short circuit or similar electrical defect occurs inthe electrical apparatus insulated. Furthermore, the electric arc whichis frequently developed in electrical equipment causes decomposition oi'the oils into gases which are inflammable and explosive.

A commercially satisfactory dielectric liquid should possess thefollowing properties. It should not sludge or be inammable. It isdesirable for many applications that the liquid should have a lowfreezing point and a high boiling point. Its viscosity should berelatively low and should not change greatly with temperature. Theliquid should be thermally and chemically stable and inert to arciing;or if sensitive to arcing it should not leave a conducting carbon path.Its ohmic resistance should be relatively high; its power :actor shouldbe relatively low `and dielectric The sludging of strength high. Itshould also have a satisfactory dielectric constant.

The primary object ci' this invention is to provide a new dielectricliquid.

Another object of my invention is to provide an improved method ofinsulating elements in electrical apparatus. 4

A further object of my invention is to provide an improved electricalapparatus containing a dielectric medium comprising a liquidorganosiloxane.

For a fuller understanding of the nature and objects of the invention,reference may be had to the following detailed description, taken inconjunction with the accompanying drawing, in which:

Fig. 1 is a view partly in side elevation and partly in section showingthe manner in which the coils and core or a transformer may be immersedin the dielectric liquids of my invention;

Fig. 2 is a View in side elevation of a capacitor having parts brokenaway to show details of the structure; and

Fig. 3 is a view in side elevation of a section of cable having partsbroken away to show details of the structure.

I have discovered that liquid organo-silicon oxide polymers, in general,possess properties which adapt them to use as dielectric liquids. Thesepolymers are compounds which contain organic radicals attached tosilicon through a carbon atom and whose silicon atoms are joined toother silicon atoms by oxygen atoms, thus Si-O-Si. They may be preparedeither by hydrolysis of hydrolyzable organo-silicanes and condensationof the hydrolysis products or by hydrolysis of a mixture of differenthydrolyzable organo-silicanes and co-condensation of the hydrolysisproducts. In the latter method of preparation, a hydrolyzable silicanewhich contains no organic radicals attached to silicon through a carbonatom, such as silicon tetrachloride or ethyl orthosilicate may beincluded along with the hydrolyzable organo-silicanes. By hydrolyzableorgano-silicanes I mean derivatives oi SiH4 which contain readilyhydrolyzable radicals such as hydrogen, halogens, amino groups, alkoxy,aroxy and acyloxy radicals, etc., the remaining valences of the siliconatoms being satisfied by organic radicals that are `iolned to thesilicon atoms through carbon atoms. Examples o'f such organic radicalsare as follows: methyl, ethyl, propyl, isopropyl, butyl, amyl, hexyl,heptyl to octadecyl and higher; alicyclic radicals such as cyclopentyl,cyclohexyl, etc.; aryl and alkaryl radicals 2 asvaoac such as phenyl,monoand poly-alkyl phenyls as tolyl, xylyl, mesityl. mono, di, andtri-ethyl phenyls, mono, di, and tripropyl phenyls, etc.; naphthyl,monoand poly-alkyl naphthyls as methyl naphthyl, diethyl naphthyl,tri-propyl nap'nthyl, etc.; tetrahydronaphthyl, anthracyl, etc.; aralkylsuch as benzyl, phenylethyl, etc.; alkenyl such as methallyl, allyl,etc., and heterocyclic radicals. The above radicals may also, ifdesired, contain certain inorganic substituents such as halogens, etc.

Hydrolysis of the above silicanes or mixtures thereof is generallyaccompanied by condensation to a greater or less degree depending uponthe conditions oi hydrolysis and the particular silicanes involved. As aresult of the hydrolysis and concurrent condensation, organo-siliconoxide polymers are produced which are partially or completely condensedand which have on the average up to and including three organic radicalsattached to each silicon atom. The polymers so obtained vary incharacter some being liquids, others being crystalline solids or gels.They also vary in the ease with which they may be further polymerized byheat since they diner in the number of active functional groups retainedas a result of incomplete hydrolysis and condensation. Those which areonly partially condensed may be converted to higher polymers and even tosolids by heat alone or even by standing at room temperature by virtueof the completion of 'the condensation. On the other hand, those whichapproach complete condensation are extremely resistant to furtherpolymerization by heat alone. However, the latter may be furtherpolymerized by proper acid treatment, alkali treatment or air treatmentas disclosed in my copencling applications Serial Number 481,155 iledMarch 30, 1943; Serial Number 481,154, filed March 30, 1943; and SerialNumber 451,354 flied July i7, 1942, all being assigned to the assigneeoi the present invention. The condensed hydrolysis products of silanesor mixtures thereof and their polymerization products are now known assiloxanes. (See page 20 of Alfred Stocks book, I-lydrides of Boron andSilicon, published 1933). This invention as shown above is concernedwith the organo-substituted siloxanes, that is those siloxanescontaining organic radicals attached to silicon through carbon-siliconlinkages.

I have found that the liquid organo-siloxanes which are substantiallycompletely condensed are to be preferred as dielectric media because oftheir great resistance to further polymerization by heat. However, thethermal stability of the partially condensed silicones may be furtherimproved by the utilization of stabilizers. In general, the liquidsiloxanes are non-hydrolyzable and substantially non-hygroscopic andbetter maintain their electrical characteristics under comparablemoisture conditions than do hydrocarbon oils. They are relativelynon-ammable and if they do burn they leave a silica ash which iselectrically nonconducting as contrasted with the conducting carbontrack of the carbon compounds. Their tendency to form sludge underordinary conditions of operation is slight. They are resistant tooxidation and have little or no eilect on metals, synthetic insulationcoatings. varnishes and rubber, even at high temperatures. They have lowfreezing points, which in many instances are far below those of thehydrocarbon oils. They also have in most cases high boiling points andconsequently lower vapor pressures. Their dash points are in generalrelatively high.

Not only is their temperature-viscosity slope relatively iiat but' theirtemperature-viscosity caemcients are constant. They possess high ohmicresistance. high dielectric strength, and low power factors. Many ofthem are excellent heat transfer media as well. Furthermore, they arecompatible with many of the common organic dielectric liquids so that,if desired, mixtures of the organo-siloxanes and other dielectricliquids may be used. In general they possess properties which incombination render them greatly superior to conventional dielectricfluids for a wide variety of applications.

The following examples illustrate representative liquid organo-siloxaneswhich possess desirable characteristics for dielectric liquids. A briefdescription of the preparation of the siloxanes is also given in eachexample for better establishing their identity.

Example 1 Trimeric phenyl ethyl silicone was prepared by the hydrolysisand condensation or phenylethylsilicon dichloride. It was a liquidhaving a viscosity of about centistokes. Its specific inductive capacitywas determined to be 2.7 and its power factor at 1 megacycle to have avalue of 0.075%. A parallel plate variable air-condenser was immersed inthe silicone and increasing potential applied across the two sets ofplates until break-down occurred. Values of 500, 1450 and 720 at a .035inch gap were noted on three successive break-downs. No deterioration ofthe silicone was apparent. With the same arrangement, break-downoccurred at 600, 625 and 700 volts with a good grade of transformer oil.

Example 2 Bis-phenyldimethylsilicyl oxide,

[CaHs (CH3) nSi] 20,

was prepared by hydrolysis and condensation ofphenyldimethylethoxysilicane. It is a liquid of low viscosity. Itsspecific inductive capacity was determined to be 2.5 while its powerfactor was .015% at 1 megacycle. Its break-down voltage over a .1 inchgap was 25 kv. on the rst test and 28.5 kv. on the fifth successivetest. After each test the liquid was stirred before making the nextmeasurement.

Example 3 A liquid copolymer having the composition 2(CHs)(C2Hs)SiO:1(CH3):SiO

was prepared in the following manner. A mixture ofdimethyldiethoxysilicane and phenylethylsilicon dichloride in the properproportions was added to a solution of water and ethanol and stirred. Anoil and aqueous layer were produced and then separated. The oil wasdissolved in ether and washed with water until acid free. The siliconewas then dried by heating fo C. under 15 mm. pressure. Its viscosity was29.6 centistokes at 25.0 C. The power factor of this silicone was 0.054%at one megacycle and room temperature and its specific inductivecapacity was 3.05. Its break-down voltage across .1 inch gap at roomtemperature and 60 cycle frequency was 34.5 kv. on the first test and29.0 kv. on the second test.

Example 4 A copolymer having the composition A 1(CHs)(CzHs)SiO:2(CHs)zSiO was prepared in a manner similar to that em.

ployed in Example 3. The liquid product had a viscosity of 23.0centistokes at 25.0 C. Its power factor at room temperature and 1megacycle frequency was approximately 0.022% while its specic inductivecapacity was 2.85. Its breakdown voltage across a .1 inch gap at roomtemperature and 60 cycle frequency was 31.7 kv. on the rst test and 23.5kv. on the second test.

Example 5 A copolymer having the composition 2 (CH3) :SiO: lCrHsSiOn/was prepared as described in Example 3, except that the water was addedto the mixture of silicanes which comprised essentially dimethyldi..ethoxysilicane and ethyltriethoxysilicane. The product was a liquidhaving a viscosity oi' 54.8 centistokes at 25.0 C. Its power factor atroom temperature and 1 megacycle frequency was approximately 0.035%while its specific inductive capacity was 2.83. Its break-down voltageacross .1 inch gap at room temperature and 60 cycle frequency was 34.0kv. on the first test and 17.5 kv. on the second test.

Example 6 A copolymer having the composition 1(CsI-Is) (CH3) aSiO%ICHaSiOM was prepared by adding a mixture ofphenyldimethylethoxysilicane and methyltriethoxysilicane in the properproportions to a .5% solution of hydrochloric acid. The oily product wastaken up in ether and washed acid free. The solvent was then removed andthe product dried. The

A copolymer comprising essentially the composition 1 (06H5) slow, :1(CH2) isioy,

was prepared by mixing phenyl silicon trichloride and a solution oftrimethylethoxysilicane in benzene and alcohol. The mixture was dilutedwith diethyl ether. Water was added with stirring, The product was takenup in ether, washed, concentrated and dried. The viscosity of theproduct at 25.0 C. was 112.3 centistokes. Its power factor at roomtemperature and 1 megacycle frequency was 0.42% while its specificinductive capacity was 3.29. Its break-down voltages across .l inch gapat room temperature and 60 cycle frequency were 29.5 kv. on the firsttest and 17.5 kv. on the second test.

Example 8 A copolymer having the composition 1(CaH5) (C2H5) SiO: 1(C21-I5) :SiO

' factor at room temperature and 1 megacycle frequency of 0.086% and aspecific inductive capacity of 2.77. Its break-down voltage across a .1inch gap at room temperature and 60 cycles was 31.0 kv. on the nrst testand 18.5 kv. on the second test.

Example 9 Liquid diethyl silicone was prepared by the hydrolysis ofdie'thylsilicon dichloride followed by condensation of the hydrolysisproduct. Its specific inductive capacity was determined to be 2.65 whileits power factor was found to be .130% at 1 megacycle and roomtemperature).L Its breakdown voltage over a .1 inch gap at roomtemperature and 60 cycle frequenyzwas 32.5 kv. on the rst test and 27.0kv. on the second test.

The liquid organo-siloxanes of my invention are well adapted to be usedas dielectric media in such electrical apparatus as transformers,capacitors, cables, switches, fuses, reactors, regulators,

circuit breakers, and similar equipment. Examples of electricalapparatus which may contain the dielectric liquids of my invention areshown in the drawing. Referring to Fig. 1 of the drawing, a transformercasing or tank i0 is shown with a core I2 carrying coils I8, allarranged in accordance with standard practice. The coils I4 are providedwith terminal conductors I8. As illustrated, the casing contains asufficient amount of the dielectric liquid I8 to completely immerse thecoils lll. Referring to Fig. 2 of the drawing, a capacitor is shown withplates 20 made of some suitable conducting material, such as aluminumfoil and the like, the plates being separated by sheets 22 of insulationor dielectric material, such as paper which is treated with a dielectricliquid of my invention. The entire assembly is supported in a casing 24and immersed in a liquid dielectric 28 of my invention. Referring toFig. 3, a cable is shown with a conductor 28 which has applied theretosome suitable insulating material 30, such as paper wrapping. A leadsheath 32 may be applied for protecting the insulation. The paperinsulation is treated with a liquid organo-siloxane of my invention.

One of the outstanding advantages yof the liquid siloxanes as dielectricmedia is their resistance to high temperature which is such that theymay be used at temperatures hitherto impossible with conventionaldielectrics. In order to take full advantage of the heat resistance ofthe liquid siloxanes, their flash points may be raised as high as 250 C.or higher either by removal of volatile lower polymers or bypolymerization of the lower polymers to higher, less volatile polymers.It should be pointed out that the flash points of these polymers are nottrue flash points but rather are the temperatures at whichdepolymerization and liberation of lower boiling polymers occurs.

In general, I have found that the properties of the liquidorgano-siloxanes may be so controlled as to fit them for a wide varietyof applications as dielectric media. Those siloxanes which have anoxygen to silicon ratio between 0.5 and 1.0 and particularly thosecontaining lower alkyl radicals have been found to be especially welladapted for use as dielectric liquids.

Whereas in some respects they may not be su.

perior to ordinary dielectrics, in other respects, they are definitelysuperior so that for many dielectric applications these liquidorgano-siloxanes represent a distinct advance over commercialdielectrics now being used.

I claim:

1. Electrical apparatus comprising, in combination, conducting elementsdisposed in spaced relationship to each other and adapted duringoperation of said apparatus to have s difference in electrical potentialtherebetween and a liquid medium interposed between said elements forinsulating one from the other, said medium comprising a liquidorgano-siloxane whose organic substituents consist essentially oforganic radicals attached to silicon through carbon-silicon linkages.

2. Electrical apparatus comprising, in combination, conducting elementsdisposed in spaced relationship to each other and adapted duringoperation of said apparatus to have a difference in electrical potentialtherebetween and a liquid medium interposed between said elements forinsulating one from the other, said medium comprising a liquidorgano-siloxane whose organic substituents consist essentially ofmono-valent hydrocarbon radicals attached to silicon throughcarbon-silicon linkages.

3. Electrical apparatus comprising, in combination, conducting elementsdisposed in spaced relationship to each other and adapted duringoperation of said apparatus to have a difference in electrical potentialtherebetween and a liquid medium interposed between said elements forinsulating one from the other, said medium consisting of a substantiallycompletely condensed liquid organo-siloxane whose organic substituentsconsist essentially of mono-valent hydrocarbon radicals attached tosilicon through carbon-silicon linkages, said organo-siloxane having anoxygen to silicon ratio of between 1/2 and one.

fi. Electrical apparatus comprising, in combination, conducting elementsdisposed in spaced relationship to each other and adapted duringoperation of said apparatus to have a difference in electrical potentialtherebetween and a liquid medium interposed between said elements forinsulating one from the other, said medium consisting of a substantiallycompletely condensed liquid organo-siloxane whose organic substituentsconsist essentially of mono-valent hydrocarbon radicals attached tosilicon through carbon-silicon linkages.

5. Electrical apparatus comprising, in combi.. nation, conductingelements disposed in spaced relationship to each other and adaptedduring operation of said apparatus to have a difference in electricalpotential therebetween and a liquid medium interposed between saidelements for insulating one from the other, said medium consistlng of asubstantially completely condensed liquid organo-siloxane whose organicsubstituents consist essentially of lower alkyl and phenyl radicalsattached to silicon through carbon-silicon linkages.

6. Electrical apparatus comprising, in combination, conducting elementsdisposed in spaced relationship to each other and adapted duringoperation of said apparatus to have a difference in electrical potentialtherebetween and a liquid medium interposed between said elements forinsulating one from the other, said medium consisting of a substantiallycompletely condensed liquid organo-siloxane whose organic substituentsconsist essentially of lower alkyl radicals attached to silicon throughcarbon-silicon linkages.

7. Electrical apparatus comprising, in combination, conducting elementsdisposed in spaced relationship to each other and adapted duringoperation of said apparatus to have a diierence in electrical potentialtherebetween and a liquid medium interposed between said elements forinsulating one from the other, said medium consisting of a liquidpolymeric phenyl ethyl silicone.

8. Electrical apparatus comprising, in comblnation, conducting elementsdisposed in spaced relationship to each other and adapted duringoperation of said apparatus to have a difference in electrical potentialtherebetween and a liquid medium interposed between said elements iorinsulating one from the other, said medium consisting of a liquidpolymeric diethyl silicone.

9. Electrical apparatus comprising, in combination, conducting elementsdisposed in spaced relationship to each other and adapted duringoperation of said apparatus to have a diierence y in electricalpotential therebetween and a liquid medium interposed between saidelements for insulating one from the other, said medium consisting ofbis-phenyl-dimethyl-silicyl oxide.

JAMES FRANKLIN HYDE.

